A plurality of accelerometers, typically two or three accelerometers, are frequently used together. For example, in inertial navigation systems two or three gyroscopes may be used in a system with two or three accelerometers to produce a reading of angular velocity, angular acceleration, angular position or a combination of those factors.
In certain stabilized systems, the sensing axes of two accelerometers may be maintained locally horizontal, and the sensing axes oriented in two directions. Typically those two directions are at right angles such as east-west and north-south. A third accelerometer may, alternatively, be positioned with its sensing axis up and down. Such an accelerometer would measure the acceleration of gravity.
When the accelerometers are not maintained with their sensing axes locally horizontal, as when they are attached to a vehicle, such a system may be characterized as a "strapped-down" system.
For purposes of this invention it is not important whether the system is a locally level system or a strapped down system. Further, the number of accelerometers is not important. Typically clusters of accelerometers contain two or three accelerometers. They may, however, contain more accelerometers as required by the user.
In precision systems, the accelerometers need to be kept at the same temperature so that the scale factor and bias remains constant. To that end, it is customary to place a temperature controller on each accelerometer. The temperature controller, typically, contains a temperature sensor, a heating or cooling element, and a servo circuit for controlling the heating or cooling element in response to a predetermined signal and the measured temperature. Thus, in a three-accelerometer system it was necessary to have three temperature controllers.
In either kind of system, it is necessary precisely to position the sensing axes of the accelerometers. To that end, an accurately positioned precision surface supports the accelerometers. On the outer case of each accelerometer is one precision mating surface which is placed in contact with the precision supporting surface. Accelerometers which are designed to measure acceleration parallel to the precision supporting surface have a precision mating surface parallel to the sensing axis of the accelerometer on the outside of the accelerometer case or housing. For example, with a horizontal supporting plate, such accelerometers could be used to measure north-south, east-west accelerations. Accelerometers which are designed to measure acceleration perpendicular to the precision supporting surface have a precision mating surface perpendicular to the sensing axis of the accelerometer on the outside of the accelerometer case or housing. For example, with a horizontal supporting surface, such accelerometers could be used to measure the vertical acceleration of gravity.
It is therefore an object of the invention to package accelerometers in an optimum manner to ensure uniform temperature among the accelerometers.
It is also an object of this invention to package an accelerometer with two precision surfaces thereon for maximum utility of the accelerometers.